Heat treatable coated article with zinc oxide inclusive contact layer(s)

ABSTRACT

A coated article is provided so as to have a fairly high visible transmission (TY or T vis ) to sheet resistance (R s ) ratio (i.e., a ratio T vis /R s ). The higher this ratio, the better the coated article&#39;s combined functionality of providing for both good solar performance (e.g., ability to reflect and/or absorb IR radiation) and high visible transmission. In certain example embodiments, coated articles herein may be heat treatable. Coated articles herein may be used in the context of insulating glass (IG) window units, architectural or residential monolithic window units, vehicle window units, and/or the like.

PRIORITY CLAIM AND CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-pan (CIP) of each of U.S. patentapplication Ser. No. 09/978,184, filed Oct. 17, 2001: and 10/314,426,filed Dec. 9, 2002, based on Provisional 60/341,837, filed Dec. 9, 2001,all of which are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

Windows including glass substrates with solar control coatings providedthereon are known in the art. Such windows may be used in the context ofarchitectural windows. insulating glass (IG) window units, automotivewindows, and/or the like.

Commonly owned US Patent Application Publication No. 2002/0.192474discloses a heat treatable (HT) low-E coating, including a pair ofsilver layers and numerous dielectric layers. While this coating iscertainly a good overall coating, usable in applications such aswindshields and architectural windows, it is problematic in certainrespects.

For example, Example 1 in 2002/0192474 has a visible transmission (TY orT_(vis)), measured monolithically, of about 69.2% before heat treatment(HT) and about 79.51 after FIT. Moreover, Example 1 of 2002/0192474 hasa sheet resistance (R_(s)) of 4.30 before HT and 2.90 after HT (takinginto account both IR reflecting silver layers). Thus, Example 1 in2002/0192474 is characterized by a ratio of visible transmission tosheet resistance (i.e., ratio T_(vis)/R_(s)) of 16.1 before HT, and 27.4after HT. Conventionally, this is a fairly high (good) ratio of visibletransmission to sheet resistance compared to many other conventionalcoated articles.

It is known that if one wants to improve a coating's solar performance(e.g., infrared reflection), the thickness of the silver layer(s) can beincreased in order to decrease the coating's sheet resistance. Thus, ifone wants to improve a coating's solar performance by increasing itsability to reflect infrared (IR) rays or the like, one typically wouldincrease the thickness of the IR blocking (or reflecting) silverlayer(s). Unfortunately, increasing the thickness of the silver layer(s)causes visible transmission (TY or T_(vis)) to drop. Accordingly, in thepast, it can be seen that when one sought to improve the solarperformance of a coating in such a manner, it was at the expense ofvisible transmission. In other words, when solar performance wasimproved, visible transmission was sacrificed and decreased. Statedanother way, it has been difficult to increase the ratio of visibletransmission to sheet resistance (i.e. T_(vis)/R_(s)), especially ifheat treatability and/or durability are to be provided. This is why manycoatings that block (reflect and/or absorb) much IR radiation haverather low visible transmission.

An excellent way to characterize a coated article's ability to bothallow high visible transmission and achieve good solar performance(e.g., IR reflection and/or absorption) is the coating's T_(vis)/R_(s)ratio. The higher the T_(vis)/R_(s) ratio, the better the combination ofthe coating's ability to both provide high visible transmission andachieve good solar performance.

As explained above, Example 1 in 2002/0192474 is characterized by aratio of visible transmission to sheet resistance (i.e., T_(vis)/R_(s))of 16.1 before HT, and 27.4 after HT, measured monolithically.

As another example, in U.S. Pat. No. 5,821,001 to Arbab, single silverExample 1 has a ratio T_(vis)/R_(s) of 10.7 before HT, and 19.5 afterHT. Double silver Example 2 of the '001 patent has a ratio T_(vis)/R_(s)of 14.4 before HT, and 22.1 after HT.

As another example, the non-heat treatable version of Example 1 of U.S.Pat. No. 6,432,545 to Schicht relates to a single silver layer stack(not a double silver stack) having a ratio T_(vis)/R_(s) of 19.8 with noHT. The heat treatable version of Example 1 of U.S. Pat. No. 6,432,545(which has a pre-HT T_(vis) of 70%) also relates to a single silverlayer stack, but has a ratio T_(vis)/R_(s) of 16.7 before HT, and 28.8after HT.

It can be seen from the above that commercially acceptable conventionalheat treatable coatings cannot achieve very high T_(vis)/R_(s) ratios,thereby illustrating that their combined characteristic of visibletransmission relative to sheet resistance (and solar performance) can beimproved.

In the past, it has been theoretically possible to increase theT_(vis)/R_(s) ratio, but not in a commercially acceptable manner. Forexample, U.S. Pat. No. 4,786,783 alleges that a coated article thereinhas a rather high T_(vis)/R_(s) ratio (the 76.4% visible transmissionalleged in this patent is suspect to some extent in view of the verythick silver layers in Example 2). However, even if one were to believethe data in the '783 patent, the coated articles therein are notcommercially acceptable.

For example, Example 2 of the '783 patent can only achieve the allegedvisible transmission of 76.4% by not including sufficient protectivedielectric layer(s) or silver protecting layer(s). For example, Example2 of the '783 patent has, inter alia, no protective contact layers(e.g., Ni, NiCr, Cr, NiCrO_(x), ZnO, Nb, or the like) between the bottomtitanium oxide layer and silver layer to protect the silver during HT(protective contact layers reduce visible transmission, but protect thesilver during HT). In other words, Example 2 of U.S. Pat. No. 4,786,783could not survive heat treatment (e.g., heat bending, tempering, and/orheat strengthening) in a commercially acceptable manner. If Example 2 ofthe '783 patent was heat treated, the sheet resistance would effectivelydisappear because the silver layer(s) would heavily oxidize and beessentially destroyed, thereby leading to unacceptable opticalproperties such as massive (very high) haze, very large ΔE* values, andunacceptable coloration. For example, because Example 2 of the '783patent does not use sufficient layer(s) to protect the silver during HT,the coated article would have very high ΔE* values (glass sidereflective and transmissive) due to heat treatment; ΔE* over 10.0 andlikely approaching 20.0 or more (for a detailed discussion on themeaning of ΔE*, see U.S. Pat. Nos. 6,495,263 and/or 6,475,626, both ofwhich are hereby incorporated herein by reference). Clearly, this is nota commercially acceptable heat treatable product.

Thus, in certain instances, it may be desirable to: (a) increase visibletransmission without sacrificing solar performance, (b) improve solarperformance without sacrificing visible transmission, and/or (c) improveboth solar performance and visible transmission. In other words, it maysometimes be desirable if the T_(vis)/R_(s) ratio could be increased, ina coating that may be heat treated in a commercially acceptable manner.For example, it may be desirable to achieve (a), (b) and/or (c) whilesimultaneously being able to keep the ΔE* value (class side reflectiveand/or transmissive) due to HT below 8.0 or the like.

BRIEF SUMMARY OF EXAMPLE EMBODIMENTS OF THE INVENTION

In certain example embodiments of this invention, there is provided aheat treatable coated article having a visible transmission (TY orT_(vis)) to sheet resistance (R_(s)) ratio (i.e., a ratio T_(vis)/R_(s))of at least 30 after heat treatment (HT), more preferably of at least 32after HT, even more preferably of at least 34 after HT, and mostpreferably of at least 36 after HT. In certain example embodiments, thecoated article is heat treatable in a commercially acceptable manner inthat: (i) its ΔE* value (glass side reflective and/or transmissive) dueto HT is no greater than about 8.0, more preferably no greater thanabout 5.0, even more preferably no greater than about 4.0, even morepreferably no greater than about 3.0, and sometimes no greater than 2.5;and/or (ii) the coating includes at least one metal inclusive contactlayer (e.g., Ni. NiCr, Cr, Ti, TiO, NiCrO_(x), ZnO, ZnAlO, Nb, mixturesthereof, or the like) between an IR reflecting layer (e.g., silverlayer) and a dielectric layer so as to protect the IR reflecting layerduring HT.

In certain example embodiments, the example non-limiting layer stacksthemselves, with respect to materials, stoichiometries and/orthicknesses may provide for the rather high ratios T_(vis)/R_(s) to becoupled with heat treatable coated articles. However, other factors mayalso be involved.

For example, in certain example embodiments, it has surprisingly beenfound that the use of a combination of a Si-rich silicon nitrideinclusive layer and a zinc oxide inclusive layer (e.g., ZnO orZnAlO_(x)) under a layer comprising silver allows the silver bedeposited (e.g., via sputtering or the like) in a manner which causesits sheet resistance to be lessened compared to if other material(s)were under the silver. In certain example embodiments, a surprisingfinding is that the Si-rich silicon nitride inclusive (Si_(x)N_(y))layer(s) allows the ratio T_(vis)/R_(s) to be increased significantlyafter HT (e.g., heat strengthening, thermal tempering, and/or heatbending). While it is not certain why this Si-rich layer Si_(x)N_(y)works in such a manner, it is believed that the presence of free Si inthe Si-rich silicon nitride inclusive layer may allow many atoms such assodium (Na) which migrate outwardly from the glass during HT to bestopped by the Si-rich silicon nitride inclusive layer before they canreach the silver and damage the same. Thus, it is believed that theoxidation caused by heat treatment allows visible transmission toincrease, and that the Si-rich Si_(x)N_(y) layer(s) reduces the amountof damage done to the silver layer(s) during FIT thereby allowing sheetresistance (R_(s)) to decrease in a satisfactory manner. Also, theSi-rich nature of this layer is believed to be responsible for thesurprise finding that coated articles herein may be heat bent to agreater extent (e.g., for a longer and/or hotter period of FIT to enabledeeper bends to be formed in the articles) than certain conventionalcoated articles.

In certain example embodiments, the Si-rich Si_(x)N_(y) layer(s) ischaracterized in that x/y may be from 0.76 to 1.5, more preferably from0.8 to 1.4, still more preferably from 0.85 to 1.2. The Si-rich layer istypically non-stoichiometric, and may include free Si therein asdeposited. Moreover, in certain example embodiments, before and/or afterFIT the Si-rich Si_(x)N_(y) layer(s) may have an index of refraction “n”of at least 2.05, more preferably of at least 2.07, and sometimes atleast 2.10 (e.g., at 632 nm).

As another example, in certain example embodiments, it has surprisinglybeen found that by depositing upper and lower zinc oxide inclusivecontact layers using different partial pressures (e.g. oxygen partialpressure), the sheet resistance of the coating can be decreased beforeand/or after HT thereby providing for improved solar performance. Incertain example embodiments, the sheet resistance of the coating (takingthe sheet resistance(s) of all silver inclusive layer(s) into account)can be reduced when the zinc oxide inclusive contact layer for the uppersilver layer is sputter deposited at a lower gas pressure than the zincoxide inclusive contact layer for the lower silver layer.

In other example embodiments of this invention the example layer stacksherein may allow for a more neutral colored (transmissive and/or glassside reflective) coated article to be provided. In certain exampleembodiments, before and/or after HT, measured monolithically, certainexample coated articles herein may have transmissive color as follows:a*_(T) from −4.5 to +1.0, more preferably from −3.0 to 0.0; and b*_(T)from −1.0 to +4.0, more preferably from 0.0 to 3.0. The transmissive b*value may be advantageous in certain example embodiments, for example,because the transmissive color is not too blue (blue becomes moreprominent as the b* value becomes more negative). If used in an IGwindow unit, the colors may change slightly. For example, thetransmissive b* values may become more positive (e.g., from 0 to 3.0) inan IG unit. With respect to glass side reflective color (as opposed totransmissive color), in certain example embodiments, before and/or afterHT and measured monolithically and/or when coupled to anothersubstrate(s), certain example coated articles herein may have glass sidereflective color as follows: a*_(G) from −4.5 to +2.0, more preferablyfrom −3.0 to 0.0; and b*_(T) from −5.0 to +4.0, more preferably from−4.0 to 3.0.

In certain example embodiments, coated articles (monolithic and/or IGunits) herein may have a SHGC (e.g. surface #2 of an IG unit) of nogreater than 0.45 (more preferably no greater than 0.41, and mostpreferably no greater than 0.40), and/or a TS % of no greater than 40%(more preferably no greater than 36%, and most preferably no greaterthan 34%).

In certain example embodiments of this invention, there is provided aheat treated coated article comprising: a multi-layer coating supportedby a glass substrate, wherein the coating comprises at least one layercomprising silver; and wherein the coated article has a ratioT_(vis)/R_(s) of at least 30 after heat treatment (where T_(vis) isvisible transmission (%) and R_(s) is sheet resistance of the coating inunits of ohms/square) and a ΔE* value (glass side reflective and/ortransmissive) of less than or equal to about 8 due to the heattreatment.

In other example embodiments of this invention, there is provided acoated article including a coating supported by a glass substrate,wherein the coating comprises from the glass substrate outwardly: alayer comprising Si-rich silicon nitride Si_(x)N_(y), where x/y is from0.85 to 1.2: a layer comprising zinc oxide contacting the layercomprising Si-rich silicon nitride; and a layer comprising silvercontacting the layer comprising zinc oxide.

In still other example embodiments of this invention, there is provideda method of making a coated article, the method comprising: providing aglass substrate: sputtering a first-zinc oxide inclusive layer over afirst layer comprising silicon nitride on the substrate using a firstoxygen partial pressure; sputtering a first layer comprising silverdirectly on the first zinc oxide inclusive layer: sputtering a secondzinc oxide inclusive layer over a second layer comprising siliconnitride on the substrate using a second oxygen partial pressure, whereinthe second zinc oxide inclusive layer is above the first zinc oxideinclusive layer; and wherein the first oxygen partial pressure isgreater than the second oxygen partial pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a monolithic coated articleaccording to an example embodiment of this invention.

FIG. 2 is a cross sectional view of the coated article of FIG. 1 beingused in an IG window unit according to an example embodiment of thisinvention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

In certain example embodiments of this invention, coated articles may beprovided so as to have a fairly high visible transmission (TY orT_(vis)) to sheet resistance (R_(s)) ratio (i.e. a ratio T_(vis)/R_(s)).The higher this ratio, the better the coated article's combinedfunctionality of providing for both good solar performance (e.g.,ability to reflect and/or absorb IR radiation) and high visibletransmission. In certain example embodiments, coated articles herein maybe heat treatable. In certain example embodiments, coated articlesherein may also be characterized by fairly neutral color (transmissiveand/or glass side reflective).

Coated articles herein may be used in the context of insulating glass(IG) window units, architectural window units, residential window units(e.g. IG and/or monolithic), vehicle window units such as laminatedwindshields, backlices, or sidelites, and/or other suitableapplications.

Coated articles herein may have one or more infrared (IR) reflectinglayers, which typically comprise or consist essentially of silver (Ag),gold (Au), or the like. Thus, this invention relates to double silverstacks (preferably), but also relates to single silver stacks, and othertypes of stacks encompassed by one or more claims.

In certain example embodiments of this invention, a coated article isprovided so as to have: (a) a visible transmission to sheet resistanceratio (i.e., a ratio T_(vis)/R_(s)) of at least 30 after heat treatment(HT), more preferably of at least 32 after HT, even more preferably ofat least 34 after HT, and most preferably of at least 36 after HT;and/or (b) a ratio T_(vis)/R_(s) of at 20 before HT, more preferably ofat least 22 before HT, even more preferably of at least 25 before HT,and most preferably of at least 28 before HT (coated articles herein mayor may not be heat treated in different embodiments). In certain exampleembodiments, coated articles are heat treatable in a commerciallyacceptable manner in that: (i) coated articles may have a ΔE* value(glass side reflective and/or transmissive) due to HT is no greater thanabout 8.0, more preferably no greater than about 5.0, even morepreferably no greater than about 4.0, even more preferably no greaterthan about 3.0, and sometimes no greater than about 2.5: and/or (ii)coatings may include at least one metal inclusive contact layer (e.g.,Ni, NiCr, Cr, Ti. TiO, NiCrO_(x), ZnO, ZnAlO, Nb, mixtures thereof, orany other suitable material) between a silver layer and a dielectriclayer so as to protect the IR reflecting layer(s) (e.g. silver or thelike) such as during HT or other processing.

Factors which may contribute to the surprisingly high T_(vis)/R_(s)ratios herein include one or more of: (a) example layer stack portionsdescribed herein. (b) example layer stoichiometries herein, (c) examplelayer thicknesses herein, (d) the use of a Si-rich silicon nitrideinclusive layer under at least one IR reflecting layer herein, and/or(e) the deposition of different zinc oxide inclusive layers at differentoxygen partial pressures.

For example, in certain example embodiments, it has surprisingly beenfound that the use of a combination of a Si-rich silicon nitrideinclusive layer and a zinc oxide inclusive layer (e.g., ZnO, ZnAlO_(x),or ZnO containing other element(s)) under a layer comprising silverallows the silver be deposited (e.g. via sputtering or the like) in amanner which causes its sheet resistance to be lessened compared to ifother material(s) were under the silver. In certain example embodiments,a surprising finding is that the Si-rich silicon nitride inclusive(Si_(x)N_(y)) layer(s) allows the ratio T_(vis)/R_(s) to be increasedsignificantly after HT (e.g., heat strengthening, thermal tempering,and/or heat bending). While it is not certain why this Si-rich layerSi_(x)N_(y) works in such a manner, it is believed that the presence offree Si in the Si-rich silicon nitride inclusive layer may allow manyatoms such as sodium (Na) which migrate outwardly from the glass duringHT to be stopped by the Si-rich silicon nitride inclusive layer beforethey can reach the silver and damage the same. Thus, it is believed thatthe oxidation caused by heat treatment allows visible transmission toincrease, and that the Si-rich Si_(x)N_(y) layer(s) reduces the amountof damage done to the silver layer(s) during HT thereby allowing sheetresistance (R_(s)) to decrease in a desirable manner.

As another example, in certain example embodiments, it has surprisinglybeen found that by depositing upper and lower zinc oxide inclusivecontact layers using different partial pressures (e.g., oxygen partialpressure), the sheet resistance of the coating can be decreased beforeand/or after HT thereby providing for improved solar performance. Incertain example embodiments, the sheet resistance of the coating (takingthe sheet resistance(s) of all silver inclusive or other IR reflectinglayer(s) into account) can be reduced when the zinc oxide inclusivecontact layer for the upper IR reflecting layer (e.g., silver) issputter deposited at a lower gas partial pressure than the zinc oxideinclusive contact layer for the lower IR reflecting layer.

Another surprising result associated with certain example embodiments ofthis invention is that neutral coloration can be provided (transmissiveand/or glass side reflective).

FIG. 1 is a side cross sectional view of a coated article according toan example non-limiting embodiment of this invention. The coated articleincludes substrate 1 (e.g., clear, green, bronze, or blue-green glasssubstrate from about 1.0 to 10.0 mm thick, more preferably from about1.0 mm to 3.5 mm thick), and coating (or layer system) 27 provided onthe substrate 1 either directly or indirectly. The coating (or layersystem) 27 may include: optional titanium oxide layer 3 (e.g., a firstdielectric layer), dielectric silicon nitride layer 4 which may beSi₃N₄, or a Si-rich type, first lower contact layer 7 which contacts andprotects IR reflecting layer 9, first conductive and potentiallymetallic infrared (IR) reflecting layer 9, first upper contact layer 11which contacts and protects IR reflecting layer 9, dielectric layer 13,another silicon nitride inclusive layer 14 (stoichiometric type orSi-rich type), second lower contact layer 17 which contacts and protectsIR reflecting layer 19, second upper contact layer 21 which contacts andprotects upper IR reflecting layer 19, dielectric layer 23, and finallyprotective dielectric layer 25. The “contact” layers 7, 11, 17 and 21each contact at least one IR reflecting layer (e.g., Ag layer). Theaforesaid layers 3-25 make up low-E (i.e., low emissivity) coating 27which is provided on glass or plastic substrate 1.

In certain preferred embodiments of this invention, the thickness oftitanium oxide layer 3 is controlled so as to allow glass sidereflective a* and/or b* values that are fairly neutral (i.e. close tozero) at high viewing angles such as 45 and/or 60 degrees. In thisrespect, the low glass side reflective a* and/or b* color valuesdescribed herein are achieved by, inter alia, controlling the thicknessof titanium oxide layer 3 so as to be from 20 to 60 Å, more preferablyfrom 30 to 60 Å, and even more preferably from 40 to 50 Å.

Infrared (IR) reflecting layers 9 and 19 are preferably metallic and/orconductive, and may comprise or consist essentially of silver (Ag),gold, or any other suitable IR reflecting material. These IR reflectinglayers help allow coating 27 to have low-E and/or good solar controlcharacteristics. The IR reflecting, layer(s) may be slightly oxidized incertain embodiments of this invention.

The upper contact layers 11 and 21 may be of or include nickel (Ni)oxide, chromium/chrome (Cr) oxide, or a nickel alloy oxide such asnickel chrome oxide (NiCrO_(x)), or other suitable material(s), incertain example embodiments of this invention. The use of, for example,NiCrO_(x) for/in these layers allows durability to be improved. TheNiCrO_(x) layers may be fully oxidized in certain embodiments of thisinvention (i.e., fully stoichiometric), or may be at least about 50%oxidized in other embodiments of this invention. While NiCrO_(x) is apreferred material for these contact layers, those skilled in the artwill recognize that other materials may instead be used. Contact layers11 and/or 21 (e.g., of or including NiCrO_(x)) may or may not beoxidation graded in different embodiments of this invention. Oxidationgrading means that the degree of oxidation in the layer(s) changesthroughout the thickness of the layer(s) so that for example a contactlayer may be graded so as to be less oxidized, at the contact interfacewith the immediately adjacent IR reflecting layer than at a portion ofthe contact layer(s) further or more/most distant from the immediatelyadjacent IR reflecting, layer. Descriptions of various types ofoxidation graded contact layers 11 and 21 are set forth in U.S.Published Patent Application No. 2002/0064662, the disclosure of whichis hereby incorporated herein by reference.

Lower contact layers 7 and 17 may comprise zinc oxide (e.g., ZnO) incertain example embodiments of this invention. The zinc oxide maycontain Al (e.g., to form ZnAlO) or other element(s) in certain exampleembodiments. In certain alternative embodiments of this invention,another layer (e.g. an oxide of NiCr, an oxide of Ni, or the like) maybe provided between the zinc oxide inclusive layer 7 (or 17) and thenearest IR reflecting layer 9 (or 19).

Silicon nitride inclusive dielectric layer(s) 4 and/or 14 is/areprovided so as to, among other things, improve heat-treatability of thecoated articles, e.g., such as thermal tempering or the like. Moreover,as explained above, in certain example embodiments, it has surprisinglybeen found that the use of a combination of a Si-rich silicon nitrideinclusive layer (4 and/or 14) and a zinc oxide inclusive layer (e.g.,ZnO or ZnAlO_(x)) (7 and/or 17) under a layer comprising silver (9and/or 19) allows the silver to be deposited (e.g., via sputtering orthe like) in a manner which causes its sheet resistance to be lessenedcompared to if certain other material(s) were under the silver. Incertain example embodiments, a surprising finding is that the Si-richsilicon nitride inclusive (Si_(x)N_(y)) layer(s) allows the ratioT_(vis)/R_(s) to be increased significantly after FIT (e.g., heatstrengthening, thermal tempering, and/or heat bending). It is believedthat the presence of free Si in the Si-rich silicon nitride inclusivelayer(s) (4 and/or 14) may allow certain atoms such as sodium (Na) whichmigrate outwardly from the glass 1 during HT to be stopped by theSi-rich silicon nitride inclusive layer before they can reach the silverand damage the same. Thus, it is believed that the oxidation caused byheat treatment allows visible transmission to increase, and that theSi-rich Si_(x)N_(y) layer(s) reduces the amount of damage done to thesilver layer(s) during FIT thereby allowing sheet resistance (R_(s)) todecrease in a satisfactory manner.

In certain example embodiments, one or both of the potentially Si-richsilicon nitride layers 4 and/or 14 may be characterized by Si_(x)N_(y)layer(s), where x/y may be from 0.76 to 1.5, more preferably from 0.8 to1.4, still more preferably from 0.85 to 1.2. Moreover, in certainexample embodiments, before and/or after HT the Si-rich Si_(x)N_(y)layer(s) (4 and/or 14) may have an index of refraction “n” of at least2.05, more preferably of at least 2.07, and sometimes at least 2.10(e.g., 632 nm) (note: stoichiometric Si₃N₄ has an index “n” of 2.04).Also, the Si-rich Si_(x)N_(y) layer(s) (4 and/or 14) in certain exampleembodiments may have an extinction coefficient “k” of at least 0.001,more preferably of at least 0.003 (note: stoichiometric Si₃N₄ has anextinction coefficient “k” of effectively 0).

Dielectric layer 13 acts as a coupling layer between the two halves ofthe coating 27, and is of or includes tin oxide in certain embodimentsof this invention. However, other dielectric materials may instead beused for layer 13.

Dielectric layers 23 and 25 may allow the environmental resistance ofthe coating 27 to be improved, and are also provided for color purposes.In certain example embodiments, dielectric layer 23 may be of or includetin oxide (e.g. SnO₂), although other materials may instead be used.Dielectric overcoat layer 25 may be of or include silicon nitride (e.g.,Si₃N₄) in certain embodiments of this invention, although othermaterials may instead be used such as titanium dioxide, siliconoxynitride, tin oxide, zinc oxide, niobium oxide, or the like such asdielectrics with an index of refraction “n” from 1.6 to 3.0. Layer 23(and/or other layers in FIG. 1) may be omitted in certain exampleembodiments of this invention.

Other layer(s) below or above the illustrated coating 27 may also beprovided. Thus, while the layer system or coating 27 is “on” or“supported by” substrate 1 (directly or indirectly), other layer(s) maybe provided therebetween. Thus, for example, coating 27 of FIG. 1 may beconsidered “on” and “supported by” the substrate 1 even if otherlayer(s) are provided between layer 3 and substrate 1. Moreover, certainlayers of coating 27 may be removed in certain embodiments, while othersmay be added between the various layers or the various layer(s) may besplit with other layer(s) added between the split sections in otherembodiments of this invention without departing from the overall spiritof certain embodiments of this invention.

FIG. 2 illustrates the coating or layer system 27 being utilized onsurface #2 of an IG window unit. Coatings 27 according to any embodimentherein may be used in IG units as shown in FIG. 2. In order todifferentiate the “inside” of the IG unit from its “outside”, the sun 29is schematically presented on the outside. The IG unit includes outsideglass pane or sheet (i.e., substrate 1 from FIG. 1) and inside glasspane or sheet 31. These two glass substrates (e.g. float glass 1-10 mmthick) are sealed at their peripheral edges by a conventional sealantand/or spacer 33 and may be provided with a conventional desiccant strip(not shown). The panes may then be retained in a conventional window ordoor retaining frame. By sealing the peripheral edges of the glasssheets and optionally replacing the air in insulating space (or chamber)30 with a gas such as argon, a typical, high insulating value IG unit isformed. Optionally, insulating space 30 may be at a pressure less thanatmospheric pressure in certain alternative embodiments (with or withouta gas in space 30), although this of course is not necessary in allembodiments. While the inner side of substrate 1 is provided withcoating 27 in FIG. 2, this invention is not so limited (e.g., coating 27may instead be provided on the interior surface of substrate 31 in otherembodiments of this invention).

Turning back to FIG. 1, while various thicknesses may be used indifferent embodiments of this invention, example thicknesses andmaterials for the respective layers on the glass substrate 1 in the FIG.1 embodiment are as follows, from the glass substrate outwardly:

TABLE 1 (Example Materials/Thicknesses; FIG. 1 Embodiment) PreferredRange More Preferred Layer ({acute over (Å)}) ({acute over (Å)}) Example(Å) TiO_(x) (layer 3) 20-400 {acute over (Å)}  20-60 {acute over (Å)} 40 Å Si_(x)N_(y) (layer 4) 50-450 Å 90-200 Å 113 Å ZnO_(x) (layer 7)10-300 {acute over (Å)} 40-150 {acute over (Å)} 100 Å Ag (layer 9)50-250 {acute over (Å)} 80-120 {acute over (Å)}  95 Å NiCrO_(x) (layer11) 10-100 {acute over (Å)}  15-35 {acute over (Å)}  26 Å SnO₂ (layer13) 0-1,000 Å  350-800 Å  483 Å Si_(x)N_(y) (layer 14) 50-450 {acuteover (Å)} 90-200 {acute over (Å)} 113 Å ZnO_(x) (layer 17) 10-300 {acuteover (Å)} 40-150 {acute over (Å)} 100 Å Ag (layer 19) 50-250 {acute over(Å)} 80-220 {acute over (Å)} 131 Å NiCrO_(x) (layer 21) 10-100 {acuteover (Å)}  15-35 {acute over (Å)}  26 Å SnO₂ (layer 23)  0-750 Å 70-200Å 100 Å Si₃N₄ (layer 25)  0-750 {acute over (Å)} 120-320 {acute over(Å)}  226 Å

In certain example embodiments of this invention, coated articles hereinmay have the following low-E (low emissivity) characteristics set forthin Table 2 when measured monolithically (before any optional HT). Thesheet resistances (R_(s)) herein take into account all IR reflectinglayers (e.g., silver layers 9, 19) in the coating, unless expresslystated to the contrary.

TABLE 2 Low-E/Solar Characteristics (Monolithic: pre-HT) CharacteristicGeneral More Preferred Most Preferred R_(s) (ohms/sq.): <=5.0 <=3.5<=3.0 E_(n): <=0.07 <=0.04 <=0.03 T_(vis)/R_(s): >=20 >=22 >=25

In certain example embodiments, coated articles herein may have thefollowing characteristics, measured monolithically for example, afterHT:

TABLE 3 Low-E/Solar Characteristics (Monolithic; post-HT) CharacteristicGeneral More Preferred Most Preferred R_(s) (ohms/sq.): <=4.5 <=3.0<=2.5  E_(n): <=0.07 <=0.04 <=0.03 T_(vis)/R_(s): >=30 >=32 >=34 (or>=36)

As explained above, the rather high values of the ratio T_(vis)/R_(s) inTables 2 and 3 are indicative of an excellent combination of highvisible transmission and good solar performance (e.g., IR reflection).These high ratio values represent significant advantages over the priorart in certain example embodiments of this invention.

Moreover, coated articles including coatings 27 according to certainexample embodiments of this invention have the following opticalcharacteristics (e.g., when the coating(s) is provided on a clear sodalime silica glass substrate 1 from 1 to 10 mm thick) (HT or non-FIT). InTable 4, all parameters are measured monolithically, unless stated tothe contrary. In Table 4 below, R_(g)Y is visible reflection from theglass (g) side of the monolithic article, while R_(f)Y is visiblereflection from the side of the monolithic article on which coating/film(f) (i.e., coating 27) is located. It is noted that the SHGC, SC, TS andultraviolet transmission characteristics are in the context of an 10Unit (not monolithic like the rest of the data in Table 4), and the ΔE*values are of course due to HT and thus taken after HT (e.g., heatstrengthening, tempering, and/or heat bending).

TABLE 4 Optical Characteristics Characteristic General More PreferredT_(vis) (or TY)(Ill. C., 2 deg.): >=70% >=75% a*_(t) (Ill. C., 2°): −4.0to +1.0 −3.0 to 0.0 b*_(t) (Ill. C., 2°): −1.0 to +4.0  0.0 to 3.0R_(g)Y (Ill. C., 2 deg.):     1 to 10%     3 to 7% a*_(g) (Ill. C., 2°):−4.5 to +2.0 −3.0 to 0.0 b*_(g) (Ill. C., 2°): −5.0 to +4.0  −4.0 to+3.0 R_(f)Y (Ill. C., 2 deg.):    1 to 7%     1 to 6% a*_(f) (Ill. C.,2°): −8.0 to 5.0  −6.0 to 3.0 b*_(f) (Ill. C., 2°): −9.0 to 10.0 −7.0 to8.0 ΔE*_(t) (transmissive): <=8.0 <=5.0, 4.0, 3.0 or 2.5 ΔE*_(g) (glassside reflective): <=8.0 <=5.0, 4.0, 3.0 or 2.5 T_(ultraviolet) (IG):<=40% <=35% SHGC (surface #2) (IG):  <=0.45 <=0.40 SC (#2) (IG):  <=0.49<=0.45 TS % (IG): <=40% <=37% Haze (post-HT): <=0.4 <=0.35

The value(s) ΔE* is important in determining whether or not there ismatchability, or substantial color matchability upon HT, in the contextof certain embodiments of this invention. Color herein is described byreference to the conventional a*, b* values. The term Δa* is simplyindicative of how much color value a* changes due to HT (the sameapplies to Δb*). If color changes too much upon HT (e.g., if ΔE* is over10), then the product may not be commercially acceptable. A very highvalue of ΔE* may also be indicated of destruction of the Ag layer duringHT, and/or of Massive haze.

The term ΔE* (and ΔE) is well understood in the art and is reported,along with various techniques for determining it, in ASTM 2244-93 aswell as being reported in Hunter et. al., The Measurement of Appearance,2^(nd) Ed. Cptr. 9, page 162 et seq. (John Wiley & Sons, 1987). As usedin the art. ΔE* (and ΔE) is a way of adequately expressing the change(or lack thereof) in reflectance and/or transmittance (and thus colorappearance, as well) in an article after or due to HT. ΔE may becalculated by the “ab” technique, or by the Hunter technique (designatedby employing a subscript “H”). ΔE corresponds to the Hunter Lab L, a, bscale (or L_(h), a_(h), b_(h)). Similarly, ΔE* corresponds to the CIELAB Scale L*, a*, b*. Both are deemed useful, and equivalent for thepurposes of this invention. For example, as reported in Hunter et. al.referenced above, the rectangular coordinate/scale technique (CIE LAB1976) known as the L*, a*, b* scale may be used, wherein:

-   -   L* is (CIE 1976) lightness units    -   a* is (CIE 1976) red-green units    -   b* is (CIE 1976) yellow-blue units

and the distance ΔE* between L*_(o) ag_(o) b*_(o) and L*₁ a*₁ b*₁ is:

ΔE*={(ΔL*)²+(Δa*)²+(Δb*)²}^(1/2)  (1)

where:

ΔL*=L* ₁ −L* _(o)  (2)

Δa*=a* ₁ −a* _(o)  (3)

Δb*=b* ₁ −b* _(o)  (4)

where the subscript “o” represents the coating (or coated article)before heat treatment and the subscript “1” represents the coating(coated article) after heat treatment; and the numbers employed (e.g.,a*, b*, L*) are those calculated by the aforesaid (CIE LAB 1976) L*, a*,b* coordinate technique. In a similar manner, \E may be calculated usingequation (1) by replacing a*, b*. L* with Hunter Lab values a_(h),b_(h), L_(h). Also within the scope of this invention and thequantification of ΔE* are the equivalent numbers if converted to thosecalculated by any other technique employing the same concept of ΔE* asdefined above.

As explained above, coated articles according to certain exampleembodiments of this invention may have a ΔE* value (glass sidereflective and/or transmissive) due to FIT which is no greater thanabout 8.0, more preferably no greater than about 5.0, even morepreferably no greater than about 4.0, even more preferably no greaterthan about 3.0, and sometimes no greater than about 2.5. These valuesare indicative of commercially acceptable heat treatable coatedarticles.

In other example embodiments of this invention, it has been found thatby thinning the bottom titanium oxide (TiO_(x), where 1<=x<=3) layer 3compared to a 75 Å thickness of a conventional coating, glass sidereflective a* color can be significantly improved (i.e., more neutral inthis case) at high viewing angles. In certain example embodiments ofthis invention, the titanium oxide layer 3 is thinned from a knownconventional 75 Å thickness to a thickness of from 20 to 60 Å, morepreferably from 30 to 60 Å, and even more preferably from 40 to 50 Å: Incertain example embodiments, such thinning of the titanium oxide layer 3allows the coated article to have color (a* and/or b*) that is moreneutral at a high viewing angle such as 45 and/or 60 degrees off-axis,than at a normal (0 degrees on-axis) viewing angle. This is advantageousin that (a) the color of the coated article is less offensive at highviewing angles (i.e., a more neutral color at angle can be achieved),and/or (b) the off-axis color of the coating may be easier toapproximately match with other coatings. In alternative embodiments ofthis invention, layer 3 need not be provided, or it may be replaced witha metal nitride inclusive layer (e.g., SiN) so that a metal nitridelayer is in direct contact with the glass.

In certain example embodiments of this invention, it has also been foundthat the respective thicknesses of the infrared (IR) reflecting layers(e.g., Ag layers) 9 and 19 may also play a part in stabilizing a* and/orb* values upon significant changes in viewing angle. In particular,making the upper IR reflecting layer at least 20 Å thicker, morepreferably at least 30 Å thicker than the lower IR reflecting layer hasbeen found to be helpful in improving color at high viewing angles insome instances. In this respect, while Table 2 above indicates the sheetresistance of the overall coating, it is noted that the sheet resistance(R_(s)) of each individual silver layer (9 and 19) may be different fromone another in certain embodiments of this invention. In certain exampleembodiments, the upper silver layer 19 has a lower sheet resistance thandoes lower silver layer 9. For example, in an example where the entirecoating has a sheet resistance (R_(s)) of 2.9 ohms/square, the uppersilver layer 19 may have a sheet resistance of 4.9 and the lower silverlayer 9 a sheet resistance of 7.0. In certain example embodiments ofthis invention, the lower silver layer 9 may have a sheet resistance(R_(s)) at least 10% higher than that of the upper silver layer 19, morepreferably at least 20% higher.

Example 1

The following examples are provided for purposes of example only, andare not intended to be limiting. The following Examples were made viasputtering so as to have approximately the layer stack set forth below,from the clear glass substrate outwardly. The listed thicknesses areapproximations:

TABLE 5 LAYER STACK FOR EXAMPLES Layer Thickness Glass Substrate about 3to 3.4 mm TiO_(x)  40 {acute over (Å)} Si_(x)N_(y) 113 {acute over (Å)}ZnAlO_(x) 100 {acute over (Å)} Ag  95 {acute over (Å)} NiCrO_(x)  26{acute over (Å)} SnO₂ 483 Å Si_(x)N_(y) 113 {acute over (Å)} ZnAlO_(x)100 {acute over (Å)} Ag 131 {acute over (Å)} NiCrO_(x)  26 {acute over(Å)} SnO₂ 100 Å Si₃N₄ 226 {acute over (Å)}

It is believed, as explained above, that the thin nature of the titaniumoxide layer is a significant factor in achieving, the fairly neutral a*and/or b* values at high viewing angles such as at 60 degrees off-axis.It is also believed that making, the upper Ag layer significantlythicker (e.g. at least 30 Å thicker) than the lower Ag layer helpsprovide neutral coloration at high viewing angles.

Moreover, as explained herein, the bottom two silicon nitride layers(Si_(x)N_(y)) are preferably non-stoichiometric and Si-rich. Asexplained above, it has been found that the use of a combination of aSi-rich silicon nitride inclusive layer and a zinc oxide inclusive layer(e.g., ZnAlO_(x)) under a layer comprising silver allows the silver tobe deposited in a manner which causes its sheet resistance to belessened (which is desirable) compared to if other material(s) wereunder the silver. In certain example embodiments, the Si-rich siliconnitride inclusive (Si_(x)N_(y)) layer(s) allows the ratio T_(vis)/R_(s)to be increased significantly after HT.

The process used in forming the coated article of Example 1 is set forthbelow. In Example 1, the bottom two silicon nitride layers were formedin a Si-rich manner, and the two nickel chrome oxide layers were formedso as to be oxidation graded as described in US 2002/0064662. The gasflows (argon (Ar), oxygen (O), and nitrogen (N)) in the below table arein units of ml/minute, and include both tuning gas and gas introducedthrough the main. The λ setting in the sputter coater is in units of mV.and as will be appreciated by those skilled in the art is indicative ofthe partial pressure of the gas being used in the sputter chamber (i.e.,a lower λ setting indicates a higher oxygen gas partial pressure). Thus,for example, a lower λ setting in the case of depositing a ZnAlO layerwould mean a higher oxygen gas partial pressure which in turn would meana less metallic (more oxidized) ZnAlO layer. The linespeed was about 5m/min. The pressures are in units of mbar×10⁻³. The cathodes used forsputtering the silver and nickel chrome oxide layers included planartargets, and the others dual C-Mag targets. The silicon (Si) targets,and thus the silicon nitride layers, were doped with about 10% aluminum(Al), so as to be indicated by SiAI targets. The Zn targets in a similarmanner were also doped with Al, so as to be indicated by ZnAl targets.The silver and nickel chrome oxide layers were sputtered using DC powersputtering, while the other layers were sputtered using a mid-frequencyAC type system.

TABLE 6 SPUTTER PROCESSING USED IN EXAMPLE 1 λ Pres- Cathode TargetPower(kW) Ar O N Setting sure C11 Ti 34.6 350 21.6 0 n/a 3.65 C12 Ti35.4 350 4.56 0 n/a 4.56 C15 SiAl 52.2 250 0 305 n/a 4.38 C24 ZnAl 43250 556 0 175 5.07 C32-a Ag 3.1 250 0 0 0 3.69 C32-b Ag 3.2 n/a 0 0 0n/a C33 NiCr 15.7 212 96 0 0 3.07 C41 Sn 46.8 200 651 75 171.4 5.30 C42Sn 44.2 200 651 75 171.4 6.68 C43 Sn 45.2 200 651 75 171.4 6.40 C44 Sn49.9 200 651 75 171.4 6.69 C45 Sn 39.8 200 651 75 171.4 5.17 C52 SiAl51.5 250 0 322 n/a 4.11 C55 ZnAl n/a 250 475 0 178 4.37 C62-a Ag 4.5 2500 0 n/a 3.43 C62-b Ag 4.6 n/a 0 0 n/a n/a C64 NiCr 14.8 250 93 0 n/a4.23 C71 Sn 41.9 200 765 75 172 5.29 C73 SiAl 54.6 225 0 430 n/a 3.93C74 SiAl 53.3 225 0 430 n/a 5.86 C75 SiAl 54.4 225 0 430 n/a 2.52

After being sputter deposited onto the glass substrate, Example 1 hadthe following characteristics after being subjected to FIT at about 625degrees C. for about 7.7 minutes, measured monolithically and in thecenter of the coated article:

TABLE 7 Characteristics of Example 1 (Monolithic-HT) CharacteristicExample 1 Visible Trans. (T_(vis) or TY)(Ill. C. 2 deg.): 81.04% a*−2.18 b* 0.93 L* 92.15 ΔE*_(t) 4.54 Glass Side Reflectance (RY)(Ill C.,2 deg.): 5.20% a* 0.06 b* −2.06 L* 27.31 ΔE*_(g) 2.44 Film SideReflective (FY)(Ill. C., 2 deg.): 4.59 a* −3.45 b* 5.64 L* 25.54 R_(s)(ohms/square) (pre-HT): 2.9 R_(s) (ohms/square) (post-HT): 2.1T_(vis)/R_(s) (post-HT): 38.6

Examples 2-4 Advantages of Si-rich

Examples 2-4 illustrate that the use of a Si-rich silicon nitridelayer(s) (4 and/or 14). Examples 2-4 were all sputter deposited inapproximately the same way as Example 1 above, except that the gas flowwas adjusted for the bottom silicon nitride layer 4 so that in Examples2-3 the bottom silicon nitride layer was Si-rich, whereas in Example 4the bottom silicon nitride layer was stoichiometric (i.e., Si₃N₄). Inthese examples, the silicon nitride layer 14 was Si-rich, and theovercoat silicon nitride layer 25 was stoichiometric. It is noted thatthe layer 4 was Si-rich in Example 1. The purpose of these Examples isto show that by making the bottom silicon nitride layer 4 silicon rich,reduced sheet resistance can be achieved especially after HT. Example 3was more Si-rich than Example 2. In the table below, HT 1 means heattreated for about 7.7 minutes in an oven at a temperature of about 650degrees C., whereas HT 2 means HT for about 5.4 minutes in an oven atabout 625 degrees C. The ratio T_(vis)/R_(s) in the table below is forHT 1.

TABLE 8 Results of Examples 2-4 Ex. R_(s) (pre-HT) T_(vis) (pre-HT)R_(s) (HT1) T_(vis) (HT1) R_(s) (HT2) T_(vis) (HT2) T_(vis)/ R_(s) 2(Si-rich) 3.2 69.3 2.3 79.35 2.3 80.16 34.50 3 (Si-rich) 3.2 69.5 2.379.69 2.3 79.00 34.64 4 (Si₃N₄) 3.3 69.7 2.4 79.17 2.4 80.16 32.98

It can be seen from the above table that the Si-rich examples (Examples2-3) for layer 4 were able to achieve lower sheet resistance values, andhigher T_(vis)/R_(s) ratios than the stoichiometric example (Example 4).

Examples 5-10 Partial Pressure Differences

Examples 5-10 are for illustrating the surprising finding that by usinga lower oxygen gas partial pressure (e.g., oxygen gas partial pressure)for the lower zinc oxide inclusive layer 7 than for the upper zinc oxideinclusive layer 17, improved (i.e., higher) T_(vis)/R_(s) ratios can beachieved. The coated articles of Examples 5-10 were deposited in thesame manner as Example 1 above, except that in Examples 5-7 the λsetting was adjusted for the bottom zinc oxide inclusive layer 7, and inExamples 8-10 the λ setting was adjusted for the top zinc oxideinclusive layer 17. As will appreciated by those skilled in the art, thelower the λ setting on the sputter coater, the less metallic theresulting layer, the more oxidized (when oxygen gas is at issue) theresulting layer, and the higher the gas (eg., oxygen) partial pressurein the sputter coater for that chamber. The heat treatment in Tablebelow was for about 5.4 minutes in an oven at about 625 degrees C. Theratios T_(vis)/R_(s) were taken after HT.

TABLE 9 Examples 5-10 λ λ R_(s) T_(vis) R_(s) T_(vis) T_(vis)/ Ex.(layer 7) (Layer 17) (pre-HT) (pre-HT) (HT) (HT) R_(s) 5 179 178 3.2369.4 2.33 80.11 34.38 6 175 178 3.18 69.5 2.31 80.48 34.84 7 183 1783.31 69.3 2.44 79.94 32.76 8 179 179 3.26 69.4 2.32 79.71 34.35 9 179174 3.28 69.2 2.46 79.86 32.46 10 179 182 3.22 69.8 2.35 80.63 34.31

From Table 9 above, it can be seen that, surprisingly, better (i.e.,higher) T_(vis)/R_(s) ratios are achievable when the lambda (λ) settingfor the lower zinc oxide inclusive layer 7 is lower (e.g., Ex. 6) andwhen the λ setting for the upper zinc oxide inclusive layer 17 is higher(e.g., Exs. 5-8 and 10). Thus, it can be seen that the bestT_(vis)/R_(s) ratios are achievable in Example 1 when the λ setting forthe lower layer 7 is lower than that of the upper layer 17. As explainedpreviously, a lower λ setting on the sputter coater translates into ahigher oxygen partial pressure, and thus a more oxidized (less metallic)zinc oxide inclusive layer. In other words, as shown in Tables 7 and 9above, the best results are achievable when the oxygen partial pressureis higher (e.g., at least 1% higher, more preferably at least 2% higher)for deposition of the lower ZnO inclusive layer 7 than for the upper ZnOinclusive layer 17.

Another surprising result associated with certain example embodiments ofthis invention is that coated articles herein may have improvedmechanical durability compared to coated articles described in US2002/0064662. While the reason for the improved durability is not clear,it is believed that the combination of the silicon nitride/zincoxide/silver may be a factor involved.

Any of the aforesaid monolithic coated articles may be used in an IGunit as shown in FIG. 2. Of course, when any of the above monolithiccoated articles are coupled with another substrate(s) to form an IGunit, transmission will drop in the resulting IG unit. Thus, in certainexample embodiments of this invention, IG units using coated articlesherein may have a visible transmission of at least about 60%, morepreferably of at least about 65%, and most preferably of at least about68%.

Certain terms are prevalently used in the glass coating art,particularly when defining the properties and solar managementcharacteristics of coated glass. Such terms are used herein inaccordance with their well known meaning. For example, as used herein:

Intensity of reflected visible wavelength light. i.e. “reflectance” isdefined by its percentage and is reported as R_(x)Y (i.e. the Y valuecited below in ASTM E-308-85), wherein “X” is either “G” for glass sideor “F” for film side. “Glass side” (e.g. “G”) means, as viewed from theside of the glass substrate opposite that on which the coating resides,while “film side” (i.e. “F”) means, as viewed from the side of the glasssubstrate on which the coating resides.

Color characteristics are measured and reported herein using the CIE LABa*, b* coordinates and scale (i.e. the CIE a*b* diagram, Ill. CIE-C, 2degree observer). Other similar coordinates may be equivalently usedsuch as by the subscript “h” to signify the conventional use of theHunter Lab Scale, or Ill. CIE-C, 10° observer, or the CIE LUV u*v*coordinates. These scales are defined herein according to ASTM D-2244-93“Standard Test Method for Calculation of Color Differences FromInstrumentally Measured Color Coordinates” Sep. 15, 1993 as augmented byASTM E-308-85, Annual Book of ASTM Standards. Vol. 06.01 “StandardMethod for Computing the Colors of Objects by 10 Using the CIE System”and/or as reported in ES LIGHTING HANDBOOK 1981 Reference Volume.

The terms “emittance” and “transmittance” are well understood in the artand are used herein according to their well known meaning. Thus, forexample, the terms visible light transmittance (TY), infrared radiationtransmittance, and ultraviolet radiation transmittance (T_(uv)) areknown in the art. Total solar energy transmittance (TS) is then usuallycharacterized as a weighted average of these values from 300 to 2500 nm(UV, visible and near IR). With respect to these transmittances, visibletransmittance (TY), as reported herein, is characterized by the standardCIE Illuminant C, 2 degree observer, technique at 380-720 nm;near-infrared is 720-2500 nm; ultraviolet is 300-380 nm; and total solaris 300-2500 nm. For purposes of emittance, however, a particularinfrared range (i.e. 2.500-40.000 nm) is employed.

Visible transmittance can be measured using known, conventionaltechniques. For example, by using a spectrophotometer, such as a PerkinElmer Lambda 900 or Hitachi U4001, a spectral curve of transmission isobtained. Visible transmission is then calculated using the aforesaidASTM 308/2244-93 methodology. A lesser number of wavelength points maybe employed than prescribed, if desired. Another technique for measuringvisible transmittance is to employ a spectrometer such as a commerciallyavailable UltraScan XE spectrophotometer manufactured by Hunter Lab.This device measures and reports visible transmittance directly. Asreported and measured herein, visible transmittance (i.e. the Y value inthe CI tristimulus system, ASTM E-308-85) uses the Ill. C., 2 degreeobserver.

Another term employed herein is “sheet resistance”. Sheet resistance(R_(s)) is a well known term in the art and is used herein in accordancewith its well known meaning. It is here reported in ohms per squareunits. Generally speaking, this term refers to the resistance in ohmsfor any square of a layer system on a glass substrate to an electriccurrent passed through the layer system. Sheet resistance is anindication of how well the layer or layer system is reflecting infraredenergy, and is thus often used along with emittance as a measure of thischaracteristic. “Sheet resistance” may for example be convenientlymeasured by using a 4-point probe ohmmeter, such as a dispensable4-point resistivity probe with a Magnetron Instruments Corp. head. ModelM-800 produced by Signatone Corp of Santa Clara, Calif.

The terms “heat treatment” and “heat treating” as used herein meanheating the article to a temperature sufficient to achieve thermaltempering, bending, and/or heat strengthening of the glass inclusivearticle. This definition includes, for example, heating a coated articlein an oven or furnace at a temperature of least about 580 or 600 degreesC. for a sufficient period to allow tempering, bending, and/or heatstrengthening. In some instances, the HT may be for at least about 4 or5 minutes, or more.

The term “shading coefficient” (SC) is a term well understood in the artand is used herein according to its well known meaning. It is determinedaccording to ASHRAE Standard 142 “Standard Method for Determining andExpressing the Heat Transfer and Total Optical Properties ofFenestration Products” by ASHRAE Standards Project Committee, SPC 142,September 1995. SC may be obtained by dividing solar heat gaincoefficient (SHGC) by about 0.87. Thus, the following formula may beused: SC=SHGC/0.87.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1-47. (canceled)
 48. A method of making a coated article, the methodcomprising: providing a glass substrate; sputtering a first zinc oxideinclusive layer over a first layer comprising silicon nitride on thesubstrate using a first oxygen partial pressure; sputtering a firstlayer comprising silver directly on the first zinc oxide inclusivelayer; sputtering a second zinc oxide inclusive layer over a secondlayer comprising silicon nitride on the substrate using a second oxygenpartial pressure, wherein the second zinc oxide inclusive layer is abovethe first zinc oxide inclusive layer; and wherein the first oxygenpartial pressure is greater than the second oxygen partial pressure. 49.The method of claim 48, wherein the first oxygen partial pressure is atleast 1% higher than the second oxygen partial pressure.
 50. The methodof claim 48, wherein the first oxygen partial pressure is at least 2%higher than the second oxygen partial pressure.
 51. The method of claim48, further comprising sputter depositing a second layer comprisingsilver over the second zinc oxide inclusive layer.
 52. The method ofclaim 51, further comprising sputter depositing a third layer comprisingsilicon nitride over the first and second layers comprising silver. 53.The method of claim 48, further comprising heat treating the glasssubstrate and the coating thereon.
 54. The method of claim 48, whereinat least the first layer comprising silicon nitride Si_(x)N_(y) isnon-stoichiometric and is Si-rich.
 55. The method of claim 54, whereinsaid first layer comprising non-stoichiometric, Si-rich silicon nitrideSi_(x)N_(y) has an index of refraction “n” of at least 2.05.
 56. Themethod of claim 48, wherein the coated article has a sheet resistance(R_(s)) of less than or equal to 4.0 after heat treatment.
 57. Themethod of claim 48, wherein the coated article has a ΔE* value (glassside reflective and/or transmissive) of less than or equal to about 4due to the heat treatment.
 58. The method of claim 48, furthercomprising a layer comprising titanium oxide between the glass substrateand the first layer comprising silicon nitride.
 59. The method of claim58, wherein the layer comprising titanium oxide has a thickness of from20 to 60 Å and is located between the glass substrate and the firstlayer comprising zinc oxide, and wherein the coated article has a TotalSolar (T_(s)) value of no greater than about 40%.
 60. The method ofclaim 48, wherein at least one of the first and second layers comprisingzinc oxide further includes aluminum.